What is knowledge?

Understanding that there various kinds of knowledge, could somone please help elaborate on the kind of direct knowledge the Buddha referred to in the context of liberation. As a conditioned being who tends to base his understanding of the world on observations, how does one differentiate between conventional knowledge and direct knowledge? While conceptually there may be an understanding of the Dhamma, how do we know if truly this is knowledge that has been realized through investigation, or merely a manifestation of a wrong view aided by the ego? Even if supported by morality and concentration how do we know if we actually know what we believe we know if the root of doubt and restlessness are the last to go?